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When searching for inspiration to create an environmentally friendly battery, University of Maryland researchers Liangbing Hu, Teng Li and their team looked to the trees. Their invention uses a tiny sliver of wood from yellow pine trees coated with tin to create a device that is a thousand times thinner than a piece of paper. Instead of lithium, they chose sodium which even though it does not store energy as efficiently, costs far less and is a much more common material. While you may not end up seeing this battery in a mobile device, it could be an ideal choice for large-scale facilities such as power plants.
Most common batteries are constructed with stiff bases that are unable to accommodate much expansion and contraction. The group at the University of Maryland found that the wood fibers they used were able to swell and contract enough to let the sodium-ion battery last for more than 400 charging cycles and out-compete a majority of other nanobatteries. After the testing cycles, lead author Hongli Zhu and colleagues saw that the fibers became wrinkled, but remained intact. Computer models led them to understand that these wrinkles relaxed stress and in the battery during charging and recharging, allowing it to survive longer. Soft enough to help buffer the strain on the changes in the tin as sodium ions are pushed through, the fibers served as the key to the battery’s success.
“Wood fibers that make up a tree once held mineral-rich water, and so are ideal for storing liquid electrolytes, making them not only the base but an active part of the battery.” said Hu. By using such inexpensive and common materials with a nod to biomimicry, the group has made great strides into reducing pollution and increasing the potential for green energy storage.
Images via the University of Maryland and Wikicommons user Walter Siegmund.